This invention relates to the soldering of electrical component leads to a printed circuit board, especially for surface mounting of electrical components.
In surface mount technology, electrical components are installed on the surface of a circuit board with the leads bonded to the surface, instead of the conventional method of having the leads pass through holes in the circuit board. One method of bonding the leads is reflow soldering, i.e. applying heat to leads which already have the correct amount of solder and thereby causing the solder to "reflow" and effect the soldered bond. To accomplish this, it is known to position the component on the board and then apply heat to solder the leads, the heat being applied by a heater bar which solders all of the leads along one side of the component simultaneously. There may be several heater bars acting simultaneously, to solder the leads projecting from other sides of the component. This can be done in an automated fashion, with the component being positioned by a robot, a pneumatic cylinder or cylinders moving the heater bar(s) downward onto the leads, and a voltage then being applied to generate the heat and solder the leads.
Conventionally, the heater bar is rigidly mounted, so that it moves straight up and down with the bar remaining horizontal. Thus if there is any angle at all on the leads, due either to the circuit board not being perfectly horizontal, or the component not sitting perfectly flat on the circuit board, or some combination, the result is that the leads opposite one end of the heater bar may not be contacted and soldered properly, while the leads opposite the other end may be damaged due to too much pressure being exerted.
The present invention responds to the need to avoid uneven pressure on the component leads during the reflow soldering.